The invention relates to a pump device for pumping an amplifying laser medium, comprising a radiation source and a multiplicity of laser diodes which emit laser beams that have parallel beam axes extending in the direction of a z axis and diverging at least two times as strongly in the direction of an x axis perpendicular to the z axis than in the direction of a y axis perpendicular to the z axis and perpendicular to the x axis, and at least one optical component having at least one cylindrical surface, with which at least some of the laser beams emitted by the laser diodes interact.
In order to pump solid-state lasers, laser diodes have recently been used increasingly instead of conventional flash lamps. A solid-state laser pumped in this way is described, for example, in Errico Armandillo and Callum Norrie: “Diode-pumped High-efficiency High-brightness Q-switched ND:YAG Slab Laser”, OPTICS LETTERS, Vol. 22, No. 15, 1 Aug. 1997, pages 1168 to 1170. Laser diodes have, in particular, advantages in terms of efficiency, pump efficiency and lifetime. In order to achieve higher pump powers, a plurality of laser diodes are combined in a common component. In the case of bars, a plurality of laser diodes (=individual emitters) are arranged on a strip-shaped chip and are operated electrically in parallel, and mounted on a common heat sink. The individual emitters of such a bar respectively emit a laser beam which has a significantly larger emission angle in the direction of a so-called fast axis, which in this document is referred to as the x axis, than in a direction perpendicular thereto of a so-called slow axis, which is referred to in this document as the y axis. For example, the divergence in the y direction is +/−5° and the divergence in the x direction is +/−33°. The beam axes of the laser beams of the laser diodes are parallel to one another and parallel to a z axis perpendicular to the x and y axes.
In laser diode stacks, a plurality of such bars are arranged with their wide sides and/or narrow sides next to one another. A commercially available laser diode stack is formed, for example, of 8 bars arranged next to one another in the x direction, with respectively 40 individual emitters spaced apart in the y direction, the emitted peak optical power being 2400 W at a wavelength of 808 nm from an emitting area of 10 mm×11.9 mm. Other numbers of bars and/or individual emitters are likewise known.
The laser radiation emitted by such a laser diode stack therefore diverges strongly, so that the imaging with optical components with which the laser radiation interacts therefore encounters limits in terms of aperture and imaging quality. In order to counteract this, it is known to arrange a microlens in the form of a cylindrical lens in front of the laser diodes of a respective bar. The cylinder axes of the microlenses are aligned in the y direction, so that the strong divergence in the x direction is reduced, for example to less than 1°. In this way, the subsequent optics for imaging the laser radiation into the amplifying laser medium are substantially simplified. However, the use of such “fast-axis collimation” microlenses leads to increased material and assembly costs (due to narrow tolerance requirements) and to power losses which, for instance, lie in the range of 10%.
Furthermore known are e.g. rod-shaped or frustopyramidal optical components extending in the z direction, the laser radiation of which is guided by means of total internal reflection to the amplifying laser medium, see for example Eric C. Honea et al.: “Analysis of an Intracavity-doubled Diode-pumped Q-switched Nd:YAG Laser Producing More Than 100 W of Power At 0.532 μm”, OPTICS LETTERS, Vol. 23, No. 15, 1 Aug. 1998, pages 1203 to 1205 and WO 2010/052308 A1. A disadvantage in this case is, in particular, the required overall length in the z direction, as a result of which the compactness of the overall laser is reduced.